usb: host: xhci: Enable pull-down on DP while port reset

Enable external pull down on DP line while port reset in progress.
This helps to reduce the voltage on D+ line in case of a high
speed detection handshake.

Change-Id: I68991d6a3dc7227036bf111c04f10ef75daa4b26
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
Signed-off-by: Vamsi Krishna Samavedam <vskrishn@codeaurora.org>